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Oct. 19, 2010 -- The season in which babies are born could affect their susceptibility to food allergies early in life, new research indicates.

Finnish scientists studied just under 6,000 children born between 2001 and 2006 in southeast Finland. About 1,000 were tested for sensitization to food allergens up to the age of 4.

Researchers say the incidence of an allergic response to certain foods varied according to season of birth, ranging from 5% for infants born in June and July to 9.5% for those entering the world in October and November.

The study says 11% of children whose 11th week in the womb occurred during April or May were sensitive to food allergens as babies and toddlers.

Pollen has something to do with this, apparently, according to the researchers from the University of Oulu in Finland.

Readings of ambient pollen for the children born between 2001 and 2006 showed that levels of birch and alder pollen peaked during April and May.

The researchers conclude that children whose first three months of fetal development ended in April or May were three times more likely to become allergic to milk and eggs than kids in the same stage of development in November and December.

Antibodies to Allergens

Previous research has shown that children born in the fall or winter are more prone to wheezing and eczema, and that they have higher levels of antibodies to allergies than kids born in spring and summer, the study researchers say.

The reason could be that fetuses start to produce antibodies to allergens around the 11th week of development and antibodies to specific allergens by 24 weeks of gestation.

An allergic type response apparently is necessary for a pregnancy to continue, and in some cases this continues after birth, according to the researchers.

The study is published online in the Journal of Epidemiology and Community Health.

The population studied comprised all 5,973 children born between April 1, 2001, and March 31, 2006; records came from the Finnish Population Register Centre.

The researchers conclude that kids whose early gestational period falls in the pollen season for broad-leafed trees are “more prone to sensitization to food allergies than other children.”

They concede that the issue is controversial and say that 18% of all children tested had developed food allergies by age 4, and that this varied by season.

“We found a higher incidence of positive results in food allergy tests among children born in October or November than among those born in other months,” and that the “incidence of such results was particularly high and especially pronounced for milk and egg among children who had their 11th gestational week in April or May, the season during which the concentrations of pollen from birch and alder are highest in the area concerned,” which was in the southeast area of Finland.

The researchers say their study is the first to examine an association between environmental pollen concentrations during the first trimester of pregnancy and the incidence of a positive result in food allergy tests.

SOURCES:News release, BMJ Group, Journal of Epidemiology and Community Health.Pyrhonen, K. Journal of Epidemiology and Community Health, October 2010.